The invention relates to a process for laminating a film under pressure and heat onto the opposite sides of a carrier, the two sides of which are heated, and to an apparatus for carrying out this process.
The process of the invention includes coating a uniform film of photoresist material onto the two sides of a carrier which is, for example, a metal board or a carrier body with metal layers vapor-deposited and/or glued on both sides.
Laminating processes are known from the preliminary published European patent application Nos. 0,040,842, 0,040,843 and 0,041,642, and in these a substrate or a carrier is laminated on both sides with a dry resist under applied pressure. The dry resist for the particular side of the carrier, for example a printed circuit board, to be laminated is drawn off from a supply roll and supplied to a pair of laminating rollers, through whose nip run the two dry resist films and the carrier located between them. Before lamination, a thin liquid layer is coated onto the surface of the carrier or the printed circuit board and forms an intermediate layer between the surface of the printed circuit board and the particular dry resist film during the laminating operation. This thin liquid layer is removed from the surface of the printed circuit board, during lamination, by being absorbed into the dry resist film.
U.S. Pat. No. 4,214,936 relates to a laminating process, in which horizontally transported boards, which are moved forwards continuously and contact-heated, are laminated on both sides, the peripheral speed of the laminating rollers being greater than the feed speed of the boards. As soon as a sensor detects the rear edge of the preheated board shortly before it enters the nip between the laminating rollers, the latter are stopped only after a certain delay time, allowing the rear edge of the board to pass through the laminating nip. As soon as the front edge of the following board is detected, the laminating rollers start to rotate again and the board which has entered the nip is laminated. This operation is repeated for each new board, and a uniform distance between the individual laminated boards is thus maintained after the nip. This results in a continuous strip composed of two dry resist layers, between which the boards are enclosed at equal distances from one another. The connecting length of the resist layers between two boards amounts, for example, to 18 mm.
In the known laminating processes, the dry resist films laminated onto the board are always supplied to the laminating station from two supply rolls, so that a double outlay is required for providing a stock of the dry resist films. Another advantage of the laminating process according to the above U.S. patent is that there is a relatively large amount of waste dry resist, since the individual boards are joined together by means of connecting pieces consisting of dry resist, and these connecting pieces have to be cut through and cut off so that the individual laminated board can undergo further processing. Because of the connecting pieces between the individual boards, there is no guarantee that the individual board will be laminated uniformly in the transitional region from the board to the connecting pieces, so that under certain circumstances, after the connecting pieces have been cut through, the photoresist will possibly come loose in the edge region of the board.